A general description of known configurations of bulk material containers is detailed in the Background section of U.S. Pat. No. 6,932,266 entitled COLLAPSIBLE BULK MATERIAL CONTAINER, issued on Aug. 23, 2005. The U.S. Pat. No. 6,932,266 also describes a number of embodiments of improved bulk material container configurations, of the type to which the present invention is specifically directed. The U.S. Pat. No. 6,932,266 is fully incorporated herein by reference.
The bulk material containers of the general type described in the U.S. Pat. No. 6,932,266 have been well received and successful in the marketplace. They generally include a forming member having a plurality of interconnected sidewalls that are configurable to form a closed outer perimeter for a 3-dimensional internal geometric volume of the container. Bottom edges of the sidewalls are designed to be supported upon and carried by a pallet. A locking mechanism or assembly is operatively connected with the forming member sidewalls and maintains the forming member sidewalls in predetermined positions relative to one another when the container is empty. While the locking mechanism can be physically separable from the sidewalls, it can also form a physical extension of the sidewalls, as for example, a mechanism that folds inwardly along the bottom edges of the sidewalls and interconnects to form a bottom surface of the assembled container. The locking assembly initially maintains the sidewalls in predetermined fixed relationship to one another around the defined internal geometric volume when operatively assembled, and prevents the sidewalls from riding or sliding upward in a direction away from the pallet or support surface for the forming member during filling of the container. The forming member is typically configured from a relatively light-weight corrugated material which can, for example, be either of cellulose or plastic construction. When configured as an extension of the forming member sidewalls, the locking assembly can also be constructed from the same corrugated material as the sidewalls. An outer open ended tubular sleeve is sized to surround and snugly engage substantially the entire outer peripheral wall areas of the forming member, and assumes the defined geometric shape of the outer surface of the forming member. The outer sleeve is preferably constructed of woven polypropylene material and provides the necessary strength for containing the bulk material within the forming member, while the forming member provides the desired shape and transport rigidity and stability for the bulk material container system. A standard bag/liner can also be placed within the internal cavity defined by the forming member as an impermeable membrane between the bulk material and forming member, to protect bulk material of the container from contamination or the environment, and/or to retain liquids or flowable bulk materials within the internal cavity. Over the time that such containers have been in the marketplace, they have been used by a wide variety of customers for containing a broad range of diverse bulk materials.
Since the overlying tubular sleeve material provides the primary containment strength for a container of the type described, a relatively thin or light-weight forming member can be used, which reduces the cost of the container. The forming member's primary function is to provide an outer peripheral shape for the container that facilities loading of bulk material into the container and provides a defined 3-dimensional container configuration that enables container stackability and stability during transport. This cooperative interrelationship between the forming member and the outer sleeve requires the outer sleeve to snugly engage the outer walls of the forming member, and to prevent the forming member from expanding beyond its rupture tolerance as forces are applied to it by the contained bulk material. This is particularly an issue thereof when peripherally joined sidewalls of an operatively folded forming member are glued together to form a generally inelastic joint. Therefore, the inner circumference dimension of an outer sleeve and the outer circumference dimension of the cooperating forming member need to be within close tolerances of one another to ensure a snug fit. The outer and inner circumference dimensions respectively of the forming members and the outer sleeves are both generally manufactured to the same nominal dimensions plus or minus (+/−) a given tolerance. Random matching of forming members with sleeves during assembly has been an issue in the manufacture and assembly of such containers. For example, the forming member is typically made from corrugated materials such as cardboard which have low operative stretchability before rupturing, and can be manufactured within fairly tight outer circumference tolerances. On the other hand, the inner circumference manufacturing tolerances of the outer sleeve have generally varied significantly more than the tolerances of the forming member. Such sleeve tolerance variances can cause an issue when, for example, an outer sleeve manufactured to its maximum inside circumferential tolerance is matched in operative overlying engagement with a forming member that is manufactured to its minimum outer circumferential tolerance. In such instances, the sleeve does not initially snugly engage the outer surface of the forming member, which can lead to rupture of the forming member as it expands from applied forces by the bulk material before the overlying sleeve can fully counteract the radial bulk material forces applied to and through the forming member.
Recognizing this relative tolerance dilemma, assemblers of the containers have been prone to use labor intensive, costly steps of measuring and hand-sorting the outer sleeve and forming members to cooperatively match the sleeves and forming members to be assembled, according to their actual sizes. For example, those forming members having a “minus” tolerance would be matched with sleeves having a “minus” tolerance or nominal dimension, but not with sleeves having a “plus” tolerance dimension. Similarly, those forming members having a “plus” outer dimensional tolerance would be matched with sleeves having a “plus” inner parameter tolerance or a nominal dimension, but not with sleeves having a “minus” dimensional tolerance. Such pre-assembly forming member and sleeve sorting and matching operations are time consuming and costly functions. Further, the preassembly sorting and matching of sleeves and forming members generally makes the container assembly process unsuitable for automation.
Since the forming members can generally be manufactured within very small tolerances, the tolerance mismatch between forming members and the outer sleeves is primarily caused by the higher (+/−) tolerance ranges of the woven tubular outer sleeve. The present invention provides an outer sleeve and a method of manufacturing such sleeve that has an accurate inner circumference that closely matches the nominal outer peripheral dimension of the forming member, eliminating the costly and burdensome process of pre-sorting and matching of sleeves to forming members, and facilitates automation of the container assembly process.